While replacement officials at NFL games this preseason have incurred plenty of grousing already from fans, players and coaches, NFL enthusiasts have also told themselves that it's just a matter of time before the regular season begins and the real zebras step up.

Unless, that is, negotiations stall further, which appears to be the case.

The NFL regular season is now expected to start with replacement officials manning the whistles due to the league and the NFL Referees Association failing to make progress on a new labor deal, ESPN reports.

The two sides are reportedly caught up on disagreements concerning not only pay but also working time — the NFL wants to make the officials commit full-time, but many already have jobs on the side that they prefer to keep. The NFL is also pushing for additional officiating crews, to increase options for the league to choose from and to build for the future, as some officials are getting up in age, ESPN reports. The referees association is opposed to that as well.

While criticism against the replacement officials was heavy in the opening week, chances are that the more preseason games they referee, the better they'll get. The NFL is banking on that to turn to the replacement officials for regular-season game duty if need be, ESPN reports.

Through the summer, both sides sounded ready to make a deal by the time the regular season started. That hope has become increasingly less likely over recent days, though.

"One source familiar with the stalled negotiations estimated that the two sides would not resolve their differences until the third week of the regular season," ESPN reports.

That sounds like one more thing NFL teams need to add into their game plans.